Alpha-amylases (alpha-1,4-glucan-4-glucanohydrolases, E.C. 3.2.1.1) constitute a group of enzymes, which catalyse hydrolysis of starch and other linear and branched 1,4-glucosidic oligo- and polysaccharides.
Among the first bacterial alpha-amylases to be used were an alpha-amylase from B. licheniformis, also known as Termamyl which has been extensively characterized and the crystal structure has been determined for this enzyme Alkaline amylases, such as the alpha-amylase derived from Bacillus sp. as disclosed in WO 95/26397, form a particular group of alpha-amylases that have found use in detergents. Many of these known bacterial amylases have been modified in order to improve their functionality in a particular application.
Methods of increasing the thermostability of alpha-amylases have been well studied. Suzuki et al. (1989) disclose chimeric alpha-amylases, in which specified regions of a B. amyloliquefaciens alpha-amylase have been substituted for the corresponding regions of a B. licheniformis alpha-amylase. The chimeric alpha-amylases were constructed with the purpose of identifying regions responsible for thermostability. Such regions were found to include amino acid residues 177-186 and amino acid residues 255-270 of the B. amyloliquefaciens alpha-amylase. Igarashi et al. 1998 show that the thermostability of AmyS-type amylases can be increased by the deletion of two amino acid residues, R179-G180, (AmyS numbering) from a loop (F 178 to A184). However, Shiau et al. (2003) showed that an AmyS enzyme with deletion in the same loop has a lower specific activity for corn starch hydrolysis at high-temperature than the parent enzyme, negating one of the principal advantages of AmyS amylases.
For environmental reasons it has been increasingly important to lower the temperature in washing, dishwashing and/or cleaning processes. However, most enzymes including amylases have a temperature optimum which is above the temperature usually used in low temperature washing. Alpha-amylase is a key enzyme for use in detergent compositions and its use has become increasingly important for removal of starchy stains during laundry washing or dishwashing. Therefore, it is important to find alpha-amylase variants, which retain their wash performance, stain removal effect and/or activity when the temperature is lowered. However, despite the efficiency of current detergents enzyme compositions, there are many stains that are difficult to completely remove. These problems are compounded by the increased use of low (e.g., cold water) wash temperatures and shorter washing cycles. Thus, it is desirable to have amylolytic enzymes that can function under low temperature and at the same time preserve or increase other desirable properties such as specific activity (amylolytic activity), stability and/or wash performance.
Thus it is an object of the present invention to provide cleaning compositions comprising alpha-amylases variants which can be used in washing, dishwashing and/or cleaning processes at low temperature, such as temperatures of 5-35° C. It is a further object of the present invention to provide alpha-amylase variants which have improved wash performance at low temperature compared to the parent alpha-amylase or compared to the alpha-amylase of any of SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12.